m0useanswered grow question an hour ago Soot or black smoke is part of many things combusting.
The temp as witch it is burning can render white ash or black and its smoke output. also things that might be adulterating the buds can do this too.
Other things that can effect burn quality is not curing the weed, having to much moisture in it. being packed to tight, not the right grind. Want it to be in the Goldilocks zone for perfect smoke. Not to tight not to loose, not to dry but not to moist, Not to chunky in grind but also not to powdery in grind.
If you grew this week you will know how it was treated and can help narrow down a bit of the options. If you bought it. Its a bit harder to do with out testing.